I may have a similar problem. It seems like the parking lights (DRL light bars but not the main headlights, plus some red tail lights) come on randomly. In my case the fob is in my pocket, but often in a room that is adjacent to the garage. But I've twice seen the lights come on (through a garage window) as I'm walking away at a larger distance. I have seen them turn off after a minute or so, but also have seen them on in the morning after apparently draining my battery of about 1 mile of range.
I have walk-away locking enabled. If I leave the fob in the house and then walk to the garage, the car is locked and all internal screens and lights are off and the mirrors are folded. Just the parking lights are on. I do not have headlights on after locking enabled.
I was thinking maybe random fob button presses while it's in my pocket. Like the first stage of Summon. Or an initial stage of auto unlock as it senses a faint fob signal but doesn't think I'm at the car just yet. I'll have to experiment a little bit with the fob to see if I can trigger the lights.